Kidney function tests explained: creatinine, urea and electrolytes

Your kidneys are the body’s filtration system, clearing waste from your blood and keeping the balance of water and salts steady. A renal function test (RFT) — sometimes called a kidney function test or U&E — checks how well that system is working. Like a lot of quiet, essential organs, kidneys rarely complain until quite late, which is why routine testing is valuable.

Creatinine and eGFR

Creatinine is a waste product from normal muscle activity that healthy kidneys filter out steadily. When kidney filtering slows, creatinine rises in the blood. From your creatinine, age and other factors, labs estimate your eGFR — an estimated glomerular filtration rate — which is a practical measure of overall kidney performance.

Urea

Urea is another waste product, made when your body breaks down protein. It is filtered by the kidneys too, so it adds a second view on filtration. Urea is also influenced by hydration and diet, so clinicians read it alongside creatinine rather than on its own.

Electrolytes

A renal panel also reports electrolytes — sodium, potassium, chloride and bicarbonate. These charged minerals keep fluid balance, nerve signalling and muscle function working, including your heartbeat. Because the kidneys help regulate them, they belong in the same picture.

• Sodium — fluid balance and nerve function.
• Potassium — muscle and heart rhythm; tightly regulated.
• Chloride and bicarbonate — the body’s acid–base balance.

The value of a baseline

A single kidney panel tells you where you stand today. Regular testing tells you the direction — and with the kidneys, direction is what matters most. ProGen Health members get these markers reviewed by a clinician and compared to their own history, so a slow change gets noticed while it is still early.